It has been known that in a lithium ion secondary battery using a carbon material as a negative electrode active material, a film is able to be formed on a negative electrode surface due to a side reaction according to a negative electrode charge reaction at the time of the first charge after the battery is manufactured. In addition, recently, it has been known that an alloy negative electrode active material or the like including silicon or tin which has been intensively studied as a negative electrode active material having high capacitance has a larger number of side reactions compared to the carbon material described above.
It has been known that lithium ions which are charged once are fixed into a negative electrode due to these side reactions, and thus all of the lithium ions are not able to be discharged, that is, irreversible capacitance occurs in which a part of the lithium ions charged in the negative electrode is not able to be discharged, and thus the capacitance of the entire battery decreases.
As the related art for solving this problem, a lithium secondary battery is disclosed in PTL 1, in which “at least one of a positive electrode, a negative electrode, and a separator includes an alkali metal powder layer formed on a surface thereof”, and the alkali metal powder layer is formed by “a step of coating an alkali metal composition to a current collector on which a high molecular film or an active material layer is formed and a step of drying the coated high molecular film or current collector”.
An object of the technology disclosed in PTL 1 is to provide “a lithium secondary battery exhibiting excellent energy density by decreasing the initial irreversible capacitance when the battery is charged and discharged”. In addition, in PTL 2, a technology is disclosed in which “a lithium powder exists on a separator surface”, and an object of this technology is to “obtain a nonaqueous electrolyte secondary battery having high initial efficiency and a high cycle retention rate”.
Further, a technology is disclosed in which “a stabilized lithium powder of which a surface is coated with a substance having excellent environment stabilization, for example, organic rubber such as nitrile butadiene rubber (NBR) and styrene butadiene rubber (SBR), an organic resin such as an ethylene vinyl alcohol copolymer resin (EVA), an inorganic compound such as metal carbonate of Li2CO3 or the like, and the like” is used as the lithium powder. Further, an object of the technology is to provide a nonaqueous electrolyte secondary battery in which an added amount of lithium is determined “after the initial efficiency of the negative electrode is obtained”, and thus “the lithium powder does not undergo metamorphosis even in a dry room at a temperature of approximately a dew point of −40° C.”, and “lithium is not precipitated on the negative electrode or capacitance does not decrease due to the excessively increased added amount of lithium”.